Selection and optimization of phase change materials for active-passive coupled battery thermal management system matching thermal shock loads

Dynamic loading makes the effective design of phase change material (PCM) coupled liquid-cooling battery thermal management systems a time-dependent optimization problem. The first step in system design is to select or configure PCM with appropriate thermophysical properties. Currently, no optimal PCM selection strategy exists for frequent thermal shock conditions, and research on the coupling relationships and substitutability among these parameters remains scarce. This study contributes two coupled parts. A methodology system integrating multi-method modelling with a six-layer interpretation and validation pipeline, and the quantitative substitution relationships among PCM thermophysical properties that this system discovers for material selection guidance. A machine learning surrogate was established to analyze the effects of C-rate, duration and four thermophysical parameters on liquid fraction, average temperature and maximum temperature, with the optimal model selected through systematic comparison. SHAP interpretation reveals that the dominant material parameter shifts with discharge stage. For liquid fraction, the governing factor shifts from specific heat capacity in the initial stage to thermal conductivity in the late stage, while for temperature responses, melting temperature gives way to thermal conductivity as the dominant parameter. Within the 0–210 s transient thermal control window, coupling relations among latent heat, melting temperature and thermal conductivity were clarified. A latent heat increase of 100 kJ/kg corresponds to a thermal conductivity rise of 0.34 W/(m·K) to maintain stable maximum temperature, whereas an opposite trend emerges when liquid fraction is considered for economic evaluation. Thermal conductivity increases by 0.1 W/(m·K) per 1 °C rise in melting temperature, providing guidance for melting thermal management design.